Lopy4 no OTAA join

I use the Lopy4 with firmware v1.15.0.b1.
With only the the OTAA code sample from https://docs.pycom.io/chapter/tutorials/lopy/lorawan-otaa.html I get no join on the TTN network. I can see the join request on the TTN console.
If I switch the lopy4 from pytrack to expension board, same result. I'm in the range of a TTN gateway, if I take my lopy(1) I do get connected tot the TTN network.